fix: wrap module script content in block scope to prevent false redeclaration errors

[Yogeshwaran C (yogeshwaran-c)]

Summary

• Fixes [html] Vscode detect wrong scope for script with type=module #229357
• When an HTML file contains classic and module scripts that declare variables with the same name, VS Code incorrectly reports "Cannot redeclare block-scoped variable" because all script contents are concatenated into a single virtual JavaScript document for validation.
• Detects <script type="module"> case-insensitively and validates classic scripts together while validating each module script as a separate ES module source document.
• Preserves source offsets for diagnostics and keeps the aggregate embedded document used by other JavaScript language features.
• Adds diagnostic-level coverage for classic/module and module/module isolation, var declarations, classic-script redeclarations, module syntax, top-level await, and diagnostic range mapping.

Test plan

• Classic and module scripts can declare the same name without a false redeclaration error.
• Multiple module scripts can declare the same name, including var, without a false redeclaration error.
• Regular scripts still report duplicate block-scoped declarations.
• Module syntax (import.meta, export) and top-level await validate without syntax errors.
• Module diagnostics map back to the correct HTML source ranges.
• HTML language server test suite passes (71 tests).

[Copilot]

Pull request overview

Attempts to isolate HTML module scripts in embedded JavaScript validation.

Changes:

• Tracks module script regions.
• Wraps module contents in braces.
• Adds embedded-document tests.

Show a summary per file

File	Description
embeddedSupport.ts	Detects and wraps module scripts.
embedded.test.ts	Tests module detection and generated content.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Medium

[Dmitriy Vasyura (dmitrivMS)]

Addressed the review feedback in 81a4f47.

The brace-based approach has been replaced with validation-specific embedded documents: classic scripts are validated together, while each <script type="module"> region is validated as a separate ES module source file. This avoids false cross-module redeclarations, also isolates var, and preserves valid module-only syntax such as export, import.meta, and top-level await. The original aggregate embedded document remains unchanged for completion, hover, rename, and other editor features, and module diagnostic offsets remain aligned with the HTML document.

The tests now exercise diagnostic behavior instead of only checking generated braces. Coverage includes classic/module and module/module duplicate names, var isolation, real classic-script redeclarations, valid module syntax, top-level await, diagnostic range mapping, and case-insensitive module type detection.

Validation: HTML language server compilation succeeded, all 70 server tests passed, and hygiene passed.

[Dmitriy Vasyura (dmitrivMS)]

Added two focused regression checks in 9920ae5: classic let versus module var isolation, and multiline module diagnostic line/column mapping. Compilation, the focused validation suite, and hygiene pass.